Aging acetic acid bacteria during

Evolution of acetic acid bacteria during winemaking and wine aging,... 

EVOLUTION OF ACETIC ACID BACTERIA DURING WINEMAKING AND WINE AGING, AND THE IMPACT ON WINE QUALITY... 

During barrel or tank aging, the wine should be protected from air to avoid both chemical and biological oxidation. In addition to oxidative yeasts, acetic acid bacteria still viable after both fermentations are capable of multiplying in the presence of air. To avoid this problem, the containers (tanks or barrels) should be filled as completely as possible. Topping off should be practiced with a wine of excellent microbiological quality to avoid contamination. An inert gas may also be used to replace the atmosphere present at the top of the tanks. 

There is no effective method for eliminating acetic acid bacteria. Current observations show that even when protected by 25-30 mg of free SO2 per liter, wines always conserve a viable bacteria population—up to 10 to 10" UFC/ml during barrel aging. Only a relatively low temperamre of around 15°C can eventually limit this problem. 

Acetic acid is always synthesized during each growth phase of the bacteria. In a series of observations, its concentration increased from 0.03 to 0.04 g/1 following rackings. These values vary greatly. They are linked to the bacteria population level and multiplication rate. For example, 0.02 g of acetic acid per liter was formed when a population was doubled from 3.5 x 10" UFC/ml to 7.0 X 10" UFC/ml. The acetic acid concentration increased by 0.08 g/1 when the initial population of 50 UFC/ml multiplied to 1.5 x 10 UFC/ml. These observations prove that acetic bacteria play a key role in the increase in volatile acidity during aging (Millet era/., 1995). 

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